This invention relates to a fluid displacement apparatus, and more particularly, to a drive mechanism a scroll type fluid displacement apparatus.
Scroll type fluid displacement apparatus are well known in the prior art. For example, U.S. Pat. No. 801,182 (Creux) discloses a device including two scrolls each having a circular end plate and a spiroidal or involute spiral element. These scrolls are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of two scrolls shifts the line contacts along the sprial curved surfaces and, as a result, the volume of the fluid pockets change. Since the volume of the fluid pockets increases or decreases dependent on the direction of the orbital motion, the scroll type fluid apparatus is applicable to compress, expand or pump fluids.
Scroll type displacement apparatus can be used as refrigeration compressors in refrigerators or air conditioning apparatus. Such compressors need high efficiency and a high compression ratio, such as a 5 to 10 compression ratio. Therefore, re-expansion volume, i.e., the smallest volume of the fluid pockets in a compression cycle, which in a scroll type compressor is located at the center of the scroll members, must be reduced as much as possible. The inner end portions of the spiral elements are thus extended inwardly to the center of the scroll members as far as possible.
Since the driving mechanism in such a high compression ratio scroll type compressor is connected to the end plate on a side surface opposite from which the spiral element extends, and the reaction force caused by the compression of gas acts at an intermediate location along the height of spiral elements of the orbiting scroll, the point at which the reaction force acts on the orbiting scroll is spaced from the point at whichthe driving force acts on the scroll. If the distance between these points is made relatively long, a moment is created which adversely effects the stability of orbital motion of the orbiting scroll.
However, when a scroll type fluid displacement apparatus requires a ratio of only 1.0 to 1.5, the re-expansion volume need not be reduced as much as in the high compression ratio application, and 1.5 to 2.0 revolutions of the spiral element is generally sufficient. A relatively large space can therefore remain unoccupied in the center of the orbiting scroll.